Tunable microwave devices with auto-adjusting matching circuit

ABSTRACT

An impedance matching circuit includes a conductor line having an input port and an output port, a ground conductor, a tunable dielectric material positioned between a first section of the conductor line and the ground conductor, a non-tunable dielectric material positioned between a second section of the conductor line and the ground conductor, and means for applying a DC voltage between the conductor line and the ground conductor. The impedance matching circuit may alternatively include a first planar ground conductor, a second planar ground conductor, a strip conductor having an input port and an output port, and positioned between the first and second planar ground conductors to define first and second gaps, the first gap being positioned between the strip conductor and the first planar ground conductor and the second gap being positioned between the strip conductor and the second planar ground conductor. A non-tunable dielectric material supports the first and second planar ground conductors and the strip conductor in the same plane. A connection is provided for applying a DC voltage between the strip conductor and the first and second planar ground conductors. A plurality of tunable dielectric layer sections are positioned between the strip conductor and the first and second planar ground conductors so as to bridge the gaps between the said first and second planar ground conductors and the strip conductor at a plurality of locations, leaving non-bridged sections in between, defining a plurality of alternating bridged and non-bridged co-planar waveguide sections.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/909,187, filed Jul. 19, 2001, which claims thebenefit of U.S. Provisional Application No. 60/219,500, filed Jul. 20,2000.

FIELD OF THE INVENTION

[0002] The invention relates to the field of tunable microwave devices.More specifically, the invention relates to impedance matching circuitsthat utilize a bias voltage to alter the permittivity of a tunabledielectric material.

BACKGROUND OF THE INVENTION

[0003] Microwave devices typically include a plurality of componentsthat may have different characteristic impedances. In order to propagatethe microwave signal through the device with minimal loss, theimpedances of the various components are matched to the characteristicimpedance of the input and output signal. By transitioning theimpedances so that an input transmission line is matched, most of theavailable power from the input is delivered to the device. Historically,impedance matching techniques have treated the matching of componentswith constant characteristic impedances to a constant characteristicimpedance of the input line, e.g. to 50 Ω. Multi-stage matching circuitshave been utilized to obtain minimal reflection loss over a specifiedfrequency range of operation of a device. Numerous techniques, such asthe use of radial stubs, quarter wave transformers, and multi-stagematching circuits with specific distributions, such as Binomial orTchebychef, etc., have been developed in order to achieve maximum powertransfer from the input to the device.

[0004] However, the characteristic impedance of the tunable componentsin tunable microwave devices is not a constant value. The characteristicimpedance of the tunable component varies over the operating range ofthe device from a minimum to a maximum impedance value. In tunabledielectric devices, a bias voltage applied to tunable dielectricmaterial provides the ability to alter the dielectric constant. Thechange in the dielectric constant provides a variation in the electricalpath length of a microwave signal. As the electrical properties of thetunable dielectric material are varied, the characteristic impedance isalso affected.

[0005] In practice, a single characteristic impedance within the tunablecomponents minimum/maximum impedance range is selected. This singleimpedance value is matched using one of the state of the art impedancematching techniques. However, as the tunable microwave device isoperated, the impedance of the tunable component varies from the matchedimpedance and a degradation in the impedance match occurs.

[0006] Prior tunable dielectric microwave transmission lines haveutilized tuning stubs and quarter wave matching transformers totransition the impedance between the input and output. The technique isbest for matching a fixed impedance mismatch. U.S. Pat. No. 5,479,139 byKoscica et al. discloses quarter wavelength transformers usingnon-tunable dielectric material for the purpose of impedance matching toa ferroelectric phase shifter device. Similar impedance matchingconfigurations using non-tunable dielectric substrate of backgroundinterest are shown in U.S. Pat. No. 5,561,407, U.S. Pat. No. 5,334,958,and U.S. Pat. No. 5,212,463. The disadvantage of the above technique isthat the impedance match is optimal at one selective tuning point of thedevice and degrades as the device is tuned through its range. Hence, thereflection loss due to impedance match increases when the device istuned away from the matched point.

[0007] Another impedance matching approach for tunable devices ispresented in U.S. Pat. No. 5,307,033 granted to Koscica et al. Thatpatent discloses the use of spacing of a half wavelength betweenelements or matching networks for the purpose of impedance matching.

[0008] Still another approach utilizes quarter wavelength transformerson tunable dielectric material as disclosed in U.S. Pat. No. 5,032,805,granted to Elmer et al. Other impedance matching configurations areshown in U.S. Pat. No. 6,029,075; 5,679,624; 5,496,795; and 5,451,567.Since it is also desirable to reduce the insertion loss of the matchingnetwork, a disadvantage of the above approach is that the quarterwavelength transformer on tunable dielectric material increases theinsertion loss.

[0009] The disclosures of all of the above-mentioned patents areexpressly incorporated by reference.

[0010] It would be desirable to minimize the impedance mismatch intunable microwave device applications. There is a need for a techniquefor improving impedance matching for tunable microwave components thatachieves minimal reflection and insertion losses throughout the range ofoperation of tunable devices.

SUMMARY OF THE INVENTION

[0011] This invention provides an impedance matching circuit comprisinga conductive line having an input port and an output port, a groundconductor, a tunable dielectric material positioned between a firstsection of the conductive line and the ground conductor, a non-tunabledielectric material positioned between a second section of the conductorline and the ground conductor, and means for applying a DC voltagebetween the conductive line and the ground conductor.

[0012] The invention further encompasses an impedance matching circuitcomprising a first ground conductor, a second ground conductor, a stripconductor having an input port and an output port. The strip conductoris positioned between the first and second ground conductors and todefine first and second gaps, the first gap being positioned between thestrip conductor and the first ground conductor and the second gap beingpositioned between the strip conductor and the second ground conductor.A non-tunable dielectric material supports the first and second groundconductors and the strip conductor in a plane. A connection point isprovided for applying a DC voltage between the strip conductor and thefirst and second ground conductors. A plurality of tunable dielectriclayer sections are positioned between the strip conductor and the firstand second ground conductors so as to bridge the gaps between the firstand second ground conductors and the strip conductor at a plurality oflocations, leaving non-bridged sections in between, defining a pluralityof alternating bridged and non-bridged co-planar waveguide sections.

[0013] The matching circuits form tunable impedance transformers thatare able to match a constant microwave source impedance connected at theinput port to a varying load impedance connected at the output port,thereby reducing signal reflections between the microwave source and avariable load impedance.

[0014] This invention provides an impedance matching circuit capable ofmatching a range of impedance values to a tunable microwave device inorder to reduce reflections from impedance mismatch during tuning of themicrowave device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a plan view of a first embodiment of the auto adjustingmatching network of this invention in the form of the microstrip;

[0016]FIG. 2 is a cross-sectional view of the embodiment of FIG. 1 takenalong line 2-2, showing a microstrip line geometry;

[0017]FIG. 3 is a cross-sectional view of the embodiment of FIG. 1 takenalong line 3-3, showing a microstrip line geometry;

[0018]FIG. 4 is a plan view of a second embodiment of the auto adjustingmatching network of this invention in the form of the stripline;

[0019]FIG. 5 is a cross-sectional view of the embodiment of FIG. 4 takenalong line 5-5, showing a stripline geometry;

[0020]FIG. 6 is a cross-sectional view of the embodiment of FIG. 4 takenalong line 6-6, showing a stripline geometry;

[0021]FIG. 7 is a cross-sectional view of a third embodiment for theauto adjusting matching network of this invention based on a coaxialgeometry;

[0022]FIG. 8 is a cross-sectional view of the embodiment of FIG. 7 takenalong line 8-8, showing the coaxial transmission line geometry;

[0023]FIG. 9 is a plan view of another embodiment for the auto adjustingmatching network of this invention including multiple partial stages ontunable material;

[0024]FIG. 10 is a plan view of another embodiment for the autoadjusting matching network of this invention based on a slotline orfinline geometry, and including multiple partial stages;

[0025]FIG. 11 is a cross-sectional view of the embodiment of FIG. 10taken along line 11-11, showing a slotline geometry;

[0026]FIG. 12 is a plan view of another embodiment for the autoadjusting matching network of this invention based on a co-planarwaveguide geometry, and including multiple partial stages;

[0027]FIG. 13 is a cross-sectional view of the embodiment of FIG. 12taken along line 13-13, showing a coplanar waveguide geometry; and

[0028]FIG. 14 is a block diagram showing a matching network of thisinvention coupled to a tunable dielectric device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The preferred embodiments described herein are each designed foruse within a certain arbitrary frequency range. For this reason allreferences to a “wavelength” will refer to the center frequency of thedesign.

[0030] Referring to the drawings, FIG. 1 is a plan view of a firstembodiment of an auto adjusting matching network of this invention inthe form of the microstrip circuit 10. FIG. 2 is a cross-sectional viewof FIG. 1 taken along line 2-2, showing the microstrip line geometry.FIG. 3 is a cross-sectional view of FIG. 1 taken along line 3-3.

[0031] The device has two ports 12 and 14 for input and output of aguided electromagnetic wave. It includes a multi-stage microstrip line16, having sections 18 and 20 of various widths and lengths, depositedon a non-tunable dielectric substrate 22, which in turn is supported byground plane 24; and a microstrip line section 26 deposited on a voltagetunable dielectric substrate 28 which in turn is supported by groundplane 30. A biasing electrode 32 in the form of a high impedancemicrostrip line is connected to microstrip section 20.

[0032] The biasing electrode 32 serves as a means for connecting anexternal variable DC bias voltage supply 34 to the auto-adjustingimpedance matching circuit. The connection of the biasing electrode 32to the circuit is not limited to microstrip section 20, but may be madeto any other part of the circuit that is electrically connected tomicrostrip line section 26. Ground planes 24 and 30 are electricallyconnected to each other. While ground planes 24 and 30 are shown asseparate elements, it should be understood that they may alternativelybe constructed as a single ground plane.

[0033] The microstrip line section 26, which comprises a conductingstrip, is directly supported by a dielectric layer 28, which is thevoltage tunable layer. A ground plane 30 supports the dielectric layer28. The microstrip line 26 is less than a quarter wavelength long andforms an approximately quarter wavelength long transformer when joinedto section 20 of the matching network on the non-tunable dielectricsubstrate 22.

[0034] The non-tunable stages 36 and 38 of the matching network 10 forma multi-stage matching circuit 40 directly supported by the non-tunabledielectric layer 22. The multi-stage matching circuit 40 can be anynumber of stages of varying widths and lengths, not limited to quarterwavelength sections. If the non-tunable and tunable substrates 22 and 28respectively are not of the same height, the last stage 38 of thematching network, which abuts the tunable dielectric 28, would beelectrically connected to microstrip line section 26 via a step 42.

[0035]FIG. 4 is a plan view of a second embodiment of the auto adjustingmatching network 44 of the invention in the form of a stripline. FIG. 5is a cross-sectional view of FIG. 4 taken along line 5-5, showing astripline geometry. FIG. 6 is a cross-sectional view of FIG. 4 takenalong line 6-6.

[0036] The device 44 has two ports 46 and 48 for input and output of theguided electromagnetic wave. It comprises a stripline 50 having sections52 and 54 of various widths and lengths embedded in a non-tunabledielectric substrate 56 supported by top and bottom ground planes 58 and60, an additional section 62 of stripline 50 embedded in a tunabledielectric substrate 64 supported by top and bottom ground planes 66 and68, and a biasing electrode 70 in the form of a high impedance striplineis connected to stripline section 54.

[0037] The connection of biasing electrode 70 to the circuit is notlimited to stripline section 54, but may be made to any other part ofthe circuit that is electrically connected to stripline section 62. Thebiasing electrode 70 serves as means for connecting the auto-adjustingimpedance matching circuit to an external adjustable DC voltage biassource 72. Ground planes 66 and 68 may or may not be the same groundplanes as for the tunable microwave device to which the matching circuitis connected. Ground planes 66 and 68 are electrically connected to theground planes of the tunable microwave device. Ground planes 66 and 68are electrically connected to ground planes 58 and 60.

[0038] The stripline section 62, which is a conducting strip, isdirectly embedded in the tunable dielectric layer 64, which is thevoltage tunable layer. Ground planes 66 on the top and 68 on the bottomsupport the dielectric layer 64. The stripline 62 is less than a quarterwavelength long and forms an approximate quarter wavelength longtransformer when joined to section 54 of the matching network in thenon-tunable dielectric substrate 56.

[0039] The non-tunable stages 76 and 78 of the matching network 44 forma multi-stage matching circuit 80 directly supported by the non-tunabledielectric layer 56. The multi-stage matching circuit 80 can be anynumber of stages of varying widths and lengths, not limited to andincluding quarter wavelength sections. The last stage 78 of the matchingnetwork, which abuts the tunable dielectric 64, is electricallyconnected to microstrip line section 62.

[0040]FIG. 7 is a longitudinal cross-sectional view of a thirdembodiment of the invention for the auto adjusting matching networkbased on a coaxial geometry. FIG. 8 is a cross-sectional view of FIG. 7taken along line 8-8, showing the coaxial transmission line geometry.

[0041] The device 82 of FIGS. 7 and 8 has two ports 84 and 86 for inputand output of the guided electromagnetic wave. It comprises a centerconductor 88 having sections 90 and 92 of various diameters and lengthssurrounded by a non-tunable dielectric substrate 94, which in turn issurrounded by ground conductor 96. An additional center conductorsection 98 is surrounded by a tunable dielectric substrate 100, which inturn is surrounded by ground conductor 102. A thin biasing electrode 104enters the co-axial structure through a small hole 106 and is connectedto the central conductor 88.

[0042] The connection of biasing electrode 104 to the circuit is notlimited to the center conductor section 92, but may be made to any otherpart of the circuit that is electrically connected to center conductorsection 98. The biasing electrode 104 serves as a means for connectingan external adjustable DC voltage bias source 74 to the auto-adjustingimpedance matching circuit. Ground conductor 102 may or may not be thesame ground conductor as for a tunable microwave device to which thematching circuit would be connected. Ground conductor 102 iselectrically connected to the ground conductor of the tunable microwavedevice. Ground conductors 96 and 102 are electrically connected to eachother.

[0043] The center conductor section 98 is surrounded by a dielectriclayer 100, which is the voltage tunable layer. The voltage tunabledielectric layer 100 is enclosed by a ground conductor 102. The centerconductor section 98 is less than a quarter wavelength long and forms acomposite impedance transformer approximately a quarter wavelength longwhen joined to section 92 of the matching network in the non-tunabledielectric 94.

[0044] The matching network 109 is a multi-stage matching circuitsurrounded by a dielectric layer 94, which is a non-tunable dielectric.The dielectric layer 94 is enclosed by a ground conductor 96. Themulti-stage matching circuit can be any number of stages of varyingwidths and lengths, not limited to and including quarter wavelengthsections. The last stage 108 of the matching circuit, which abuts thetunable dielectric 100, is electrically connected to the centerconductor 98.

[0045] An extension to the first embodiment is shown in FIG. 9, as amatching circuit having multiple tunable stages 112, 114, 116, andmultiple non-tunable stages 154, 156, 114 a and 116 a. The device hastwo ports 118 and 120 for input and output of a guided electromagneticwave. It includes a matching microstrip line section 122, deposited on anon-tunable dielectric substrate 124; multiple pairs of microstripsections 126, 128 and 130, 132 and 134, 136 deposited on pairs ofnon-tunable and tunable dielectric substrates 124, 138 and 140, 142 and144, 146 respectively; a biasing electrode 148 in the form of a highimpedance microstrip line connected to microstrip section 126; and aground plane (not shown). The dielectric substrates are supported by theground plane, which may include different electrically connectedsections to adapt to the different thicknesses of the substrates 124,140 144 and 138, 142, 146.

[0046] The connection of biasing electrode 148 to the circuit is notlimited to microstrip section 126, but may be made to any other part ofthe circuit that is electrically connected to microstrip line sections128, 132 and 136. The biasing electrode 148 connects the auto-adjustingimpedance matching circuit to an adjustable DC voltage bias source 152.The ground plane may or may not be the same ground plane as for thetunable microwave device to which the matching circuit is connected.

[0047] Each of the microstrip line sections 128, 132 and 136 is lessthan a quarter wavelength long and forms an approximately quarterwavelength long impedance transformer when joined to microstrip sections126, 130 and 134 respectively.

[0048] The non-tunable stages of the matching network 154, 156 form amulti-stage matching circuit 158 directly supported by the non-tunabledielectric layer 124. The multi-stage matching circuit can be any numberof stages of varying widths and lengths, not limited to quarterwavelength sections. Microstrip section 126 of the last stage 156 of thenon-tuning part of the matching network, which abuts the tunable stage112, is electrically connected to microstrip line section 128. Thelatter abuts non-tunable tunable stage 114 a and is electricallyconnected to microstrip line section 130. The latter abuts tunable stage114 and is electrically connected to microstrip line section 132. Thelatter abuts non-tunable tunable stage 134 and is electrically connectedto microstrip line section 134. The latter abuts tunable stage 116 andis electrically connected to microstrip line section 136.

[0049] The multiple stage pairs in FIG. 9 ensure impedance matching overa wider frequency and impedance range than the more simple geometry ofFIG. 1. It should be understood that a similar extension to multiplestage pairs can be made for the second (stripline) and third (co-axial)embodiments as well.

[0050]FIG. 10 is a plan view of another embodiment for the autoadjusting matching network 160 based on a slotline or finline geometry,and including multiple partial stages 162, 164, and 166. FIG. 11 is across-sectional view of FIG. 10 taken along line 11-11, showing aslotline geometry.

[0051] The device 160 has two ports 168 and 170 for input and output ofthe guided electromagnetic wave. It includes two conducting coplanarconductors 172 and 174, supported by non-tunable dielectric layer 176,and separated by a gap 178 to form a slotline (or finline if integratedinto a waveguide) geometry. For comparison with the first, second andthird embodiments, one of these coplanar conductors 174 can beconsidered to be the ground conductor. The slot 178 may be of uniformwidth, or it can be of non-uniform width as shown in FIG. 10. Atmultiple locations (three shown in FIG. 10) 162, 164 and 166, the slotis bridged by a tunable dielectric layer 180, 182 and 184, which can bedeposited on the supporting dielectric layer 176 using thick or thinfilm technology prior to depositing the metal layers 172 and 174 on thesupporting dielectric layer 176. Between locations 162, 164 and 166,there remain sections 186 and 188 as well as 190 a and 190 b, which arenot bridged with a tunable material layer. Planar conductor 172 isconnected to an adjustable DC voltage bias source 192, and planarconductor 174 is connected to DC ground. The coplanar conductors may ormay not be the same coplanar conductors as for the tunable microwavedevice to which the matching circuit is connected.

[0052] Each of the tunable slotline sections 162, 164 and 166 is lessthan a quarter wavelength long, but together with the non-tunableintermediate sections 186, 188, 190 a and 190 b which are also typicallyshorter than a quarter wavelength long, these cascaded slotline sectionsform a cascaded network that may be a multiple of quarter wavelengthslong. The network can be made longer by simply adding more pairs oftunable and non-tunable slotline sections. By careful choice of therelative lengths of each tunable and non-tunable slotline section, thecascaded network forms a tunable impedance matching network over a widefrequency band.

[0053] The slotline sections 186, 188 190 a and 190 b may also bebridged by a tunable layer, similar to the tunable sections 162, 164 and166, but which may be less tunable. Reduced tunability in regions 186,188 190 a and 190 b can be achieved by using a material that is lesstunable and/or by using wider slot gaps to reduce the bias fieldstrength in these regions. Instead of using different types of materialsin the strongly tunable and lesser tunable slot regions, a tunablematerial can be deposited which may have varying tunability along theslot length.

[0054]FIG. 12 is a plan view of another embodiment for the autoadjusting matching network 194 based on a co-planar waveguide geometry,and including multiple partial stages. FIG. 13 is a cross-sectional viewtaken along line 13-13 in FIG. 12, showing a coplanar waveguidegeometry.

[0055] The device 194 has two ports 196 and 198 for input and output ofthe guided electromagnetic wave. It includes two coplanar conductingground conductors 200, 202 and a central strip conductor 204, supportedby non-tunable dielectric layer 206, and separated by gaps 208 and 210to form a co-planar waveguide geometry. The slots 208 and 210 may be ofuniform width, or they can be of non-uniform width as shown in FIG. 12.At multiple locations 212, 214 and 216, the slots 208 and 210 arebridged by a tunable dielectric layers 218 220 and 222, which can bedeposited on the supporting dielectric layer 206 using thick or thinfilm technology prior to depositing the metal layers 200 and 202 and 204on the supporting dielectric layer 206. Between locations 212, 214 and216, there remain sections 224, 226 as well as 228 a and 228 b, whichare not bridged with a tunable material layer. Strip conductor 204 isconnected to an adjustable DC voltage bias source 230, and planar groundconductors 200 and 202 are connected to DC ground. The coplanarconductors 200 and 202 and strip 204 may or may not be the same coplanarconductors as for the tunable microwave device to which the matchingcircuit is connected.

[0056] Each of the tunable co-planar waveguide sections 212, 214 and 216is less than a quarter wavelength long, but together with thenon-tunable intermediate sections 224, 226, 228 a and 228 b, which arealso typically shorter than a quarter wavelength long, these cascadedco-planar waveguide sections form a cascaded network that may be amultiple of quarter wavelengths long. The network can be made longer bysimply adding more pairs of tunable and non-tunable co-planar waveguidesections. By careful choice of the relative lengths of each tunable andnon-tunable section, the cascaded network forms a tunable impedancematching network over a wide frequency band.

[0057] The slots in co-planar waveguide sections 224, 226, 228 a and 228b may also be bridged by a tunable layer, similar to the tunablesections 212, 214 and 216, but in that case the layer may be lesstunable. Reduced tunability in regions 224, 226, 228 a and 228 b can beachieved by using a material that is less tunable and/or by using widerslot gaps to reduce the bias field strength in these regions. Instead ofusing different types of materials in the strongly tunable and lessertunable slot regions, a tunable material can be deposited which may havevarying tunability along the co-planar waveguide length.

[0058]FIG. 14 is a block diagram showing a matching network 10constructed in accordance with this invention coupled to a tunablemicrowave device 232. The tunable microwave device 232 could be one ofmany devices which have varying input/output characteristic impedancessuch as tunable phase shifters, delay lines, filters, etc. In thearrangement shown in FIG. 14, the adjustable external DC voltage sourceis used to supply bias voltage to the matching network 10 and thetunable microwave device 232 in tandem. As the voltage supplied by theexternal DC voltage source changes, the characteristic input/outputimpedance of the tunable dielectric device will also change. At the sametime the impedance characteristics of the matching network will changeto maximize power transfer from/to the microwave source/load 234 to/fromthe tunable microwave device 232. Alternatively, the tunable microwavedevice 232 and the matching network 10 can be controlled by twodifferent external DC voltage sources.

[0059] The first preferred embodiment of the auto adjusting matchingnetwork uses a microstrip geometry. The second preferred embodiment ofthe auto-adjusting matching circuit has a stripline geometry, the thirdhas a coaxial geometry, the fourth has a slotline or finline geometryand the fifth has a co-planar waveguide geometry.

[0060] In some embodiments, this invention provides a multi-stageimpedance circuit functionally interposed between a conductor line andan entry point of a tunable microwave device, wherein the multi-stageimpedance matching circuit reduces the signal reflection of a microwavesignal propagating through the tunable impedance transformer into themicrowave device, by matching the wave impedance of a microwave signalat the entry point, to the microwave source impedance.

[0061] This invention provides electrically controlled auto-adjustingmatching networks that contribute to the tunable applications ofmicrowave devices, while improving upon the range of operation of suchdevices. It overcomes the problem of matching to a microwavetransmission line with a varying characteristic impedance. It is wellsuitable for tunable phase shifters, delay lines, and impedance matchingfor power amplifiers used as general-purpose microwave components in avariety of applications such as handset power amplifiers, radar,microwave instrumentation and measurement systems and radio frequencyphased array antennas. The devices are applicable over a wide frequencyrange, from 500 MHz to 40 GHz.

[0062] The invention provides an impedance matching circuit havingminimal reflection loss and reduced insertion loss over the tuning rangeof the device.

[0063] The auto-adjusting matching circuits of this invention may have adual function. The main objective of the auto-adjusting matching circuitis to operate as an impedance matching network. Additionally, theauto-adjusting matching circuit has the ability to contribute to thetunable range of the microwave device to which it is coupled. Hence, theauto-adjusting matching circuit may incorporate tunable applications inits design as well. For example, the length of a tunable phase shiftermay be decreased since the matching network provides a small amount oftunable phase shift through its operating range. Thus, both objectivesalso lead to a decrease in the insertion loss.

[0064] The present invention is advantageous because it has wideapplication to tunable microwave transmission line applications thatmake use of a static electric field to produce the desired tuningeffect. This invention is also applicable to tunable microwave deviceapplications that operate over a frequency band or at a singlefrequency.

[0065] The auto-adjusting matching circuit according to the presentinvention may or may not contribute to the design criteria of thetunable application and may use a common DC Voltage bias or a differentDC Voltage bias. The invention minimizes reflection loss and increasesthe useable bandwidth of the microwave application.

[0066] The auto-adjusting matching circuit is a multi-stage impedancematching circuit that includes both non-tunable and tunable dielectricmaterial. For example in one preferred embodiment, the impedancematching transformer stage supported by the tunable dielectric materialis less than a quarter wavelength long and is connected to the adjacenttransformer supported by the non-tunable dielectric to form a compositequarter wavelength impedance transformer. Individual sections of such acomposite quarter wave transformer can be referred to as “partialstages”. The matching transformers are tuned in tandem with themicrowave device, in order to obtain low insertion loss as well asreducing the reflections from impedance mismatch. Thus, minimalinsertion loss in the matching network is achieved. Additionally, thereflections from impedance mismatch due to the tuning of the microwavedevice are also minimized.

[0067] The auto-adjusting matching circuit is a two-port device, whichin its simplest form includes a conducting matching network supported bya low-loss, conventional non-tunable dielectric substrate which in turnis a supported by a first ground conductor; at least one conductingpartial-stage supported by a low-loss voltage-tunable dielectric layer,which in turn is supported by a second ground conductor; and a biasingelectrode for connection to an external variable DC voltage source,preferably by way of a microwave choke.

[0068] The partial-stage on the tunable dielectric layer and theadjoining partial stage on the non-tunable dielectric layer together canform an approximate quarter wavelength long impedance transformer. Theport leading to the partial stage supported by the tunable dielectriccan be connected at the input or output of a tunable microwave device.The other port of the auto-adjusting matching circuit, which isconnected to the matching section supported by the non-tunabledielectric substrate, forms a microwave signal input/output port, whichhas a substantially constant characteristic impedance.

[0069] The low-loss voltage-tunable dielectric layer of thepartial-stage of the matching circuit may be comprised of the sametunable dielectric material as the tunable microwave device to which itis connected, or it may be comprised of a different tunable dielectricmaterial. The auto-adjusting matching circuit may be biased with thesame bias voltage as the tunable microwave device to which it isconnected, or it may have a separate bias voltage applied. If more thanone tunable material is used, i.e. one tunable dielectric material forthe microwave tunable device and another for the partial-stage of thematching circuit, each may have its own separate bias voltage source oruse a common (shared) bias voltage source.

[0070] As is well known, the bandwidth of the impedance matching networkmay be improved by additional matching stages. The additional matchingstages may each be comprised of a partial stage supported by a tunabledielectric substrate in series with a partial stage supported by anon-tunable dielectric substrate. The tunable dielectric substratesections for the additional matching stages may be comprised of the sametunable dielectric material as the first tunable partial-stage, or itmay be comprised of a different tunable dielectric material.

[0071] The microwave matching section, which is supported by the tunabledielectric substrate for the dual purpose of reducing signal reflectionsand providing good transmission to and from the microwave transmissionline application as well as contributing to the tunability of theapplication, may be a partial stage less than a quarter wave lengthlong, or may include more than one matching section and is not limitedto the use of one tunable dielectric substrate.

[0072] The biasing electrode may be connected to the auto-adjustingmatching circuit by way of a microwave choke such as a high impedancetransmission line, or by a highly inductive wire attached directly tothe auto-adjusting matching circuit at any point that is ultimatelyelectrically connected to the partial stage supported by the tunabledielectric.

[0073] The first and second ground conductors are electrically connectedand if both are of a planar construction, they should preferably formone continuous ground plane. The non-tunable matching stages areelectrically connected to the tunable partial-stage.

[0074] The objective of a matching network is to ensure that a guidedelectromagnetic wave entering one port (as such defined as the inputport) will enter the microwave device and leave it at the other port(output), with minimum residual reflections at each port. The groundplane is kept at zero voltage, while a voltage bias is applied to theelectrodes. The voltage bias causes a DC electric field across thevoltage tunable dielectric, which affects the dielectric permittivity ofthe medium. Since the characteristic impedance of the microstrip isinversely proportional to the square root of the effective dielectricpermittivity of the medium around the strip, the biasing voltage can beused to control the characteristic impedance of the auto-adjustingmatching network. In this way, the characteristic impedance of theinvention can be controlled by the voltage bias. The advantages of thisinvention are low insertion loss and improved bandwidth operation fortunable devices.

[0075] Tunable dielectric materials have been described in severalpatents. Barium strontium titanate (BaTiO₃—SrTiO₃), also referred to asBSTO, is used for its high dielectric constant (200-6,000) and largechange in dielectric constant with applied voltage (25-75 percent with afield of 2 Volts/micron). Tunable dielectric materials including bariumstrontium titanate are disclosed in U.S. Pat. No. 5,427,988 by Sengupta,et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-MgO”;U.S. Pat. No. 5,635,434 by Sengupta, et al. entitled “CeramicFerroelectric Composite Material-BSTO-Magnesium Based Compound”; U.S.Pat. No. 5,830,591 by Sengupta, et al. entitled “MultilayeredFerroelectric Composite Waveguides”; U.S. Pat. No. 5,846,893 bySengupta, et al. entitled “Thin Film Ferroelectric Composites and Methodof Making”; U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled “Methodof Making Thin Film Composites”; U.S. Pat. No. 5,693,429 by Sengupta, etal. entitled “Electronically Graded Multilayer FerroelectricComposites”; U.S. Pat. No. 5,635,433 by Sengupta entitled “CeramicFerroelectric Composite Material BSTO-ZnO”; U.S. Pat. No. 6,074,971 byChiu et al. entitled “Ceramic Ferroelectric Composite Materials withEnhanced Electronic Properties BSTO-Mg Based Compound-Rare Earth Oxide”.These patents are incorporated herein by reference.

[0076] The electronically tunable materials that can be used in thepresent invention include at least one electronically tunable dielectricphase, such as barium strontium titanate, in combination with at leasttwo additional metal oxide phases. Barium strontium titanate of theformula Ba_(x)Sr_(1-x)TiO₃ is a preferred electronically tunabledielectric material due to its favorable tuning characteristics, lowCurie temperatures and low microwave loss properties. In the formulaBa_(x)Sr_(1-x)TiO₃, x can be any value from 0 to 1, preferably fromabout 0.15 to about 0.6. More preferably, x is from 0.3 to 0.6.

[0077] Other electronically tunable dielectric materials may be usedpartially or entirely in place of barium strontium titanate. An exampleis Ba_(x)Ca_(1-x)TiO₃, where x is in a range from about 0.2 to about0.8, preferably from about 0.4 to about 0.6. Additional electronicallytunable ferroelectrics include Pb_(x)Zr_(1-x)TiO₃ (PZT) where x rangesfrom about 0.05 to about 0.4, lead lanthanum zirconium titanate (PLZT),PbTiO₃, BaCaZrTiO₃, NaNO₃, KNbO₃, LiNbO₃, LiTaO₃, PbNb₂O₆, PbTa₂O₆,KSr(NbO₃) and NaBa₂(NbO₃)5KH₂PO₄.

[0078] In addition, the following U.S. Patent Applications, assigned tothe assignee of this application, disclose additional examples oftunable dielectric materials: U.S. application Ser. No. 09/594,837 filedJun. 15, 2000, entitled “Electronically Tunable Ceramic MaterialsIncluding Tunable Dielectric and Metal Silicate Phases”; U.S.application Ser. No. 09/768,690 filed Jan. 24, 2001, entitled“Electronically Tunable, Low-Loss Ceramic Materials Including a TunableDielectric Phase and Multiple Metal Oxide Phases”; U.S. application Ser.No. 09/882,605 filed Jun. 15, 2001, entitled “Electronically TunableDielectric Composite Thick Films And Methods Of Making Same”; and U.S.Provisional Application Serial No. 60/295,046 filed Jun. 1, 2001entitled “Tunable Dielectric Compositions Including Low Loss GlassFrits”. These patent applications are incorporated herein by reference.

[0079] The tunable dielectric materials can also be combined with one ormore non-tunable dielectric materials. The non-tunable phase(s) mayinclude MgO, MgAl₂O₄, MgTiO₃, Mg₂SiO₄, CaSiO₃, MgSrZrTiO₆, CaTiO₃,Al₂O₃, SiO₂ and/or other metal silicates such as BaSiO₃ and SrSiO₃. Thenon-tunable dielectric phases may be any combination of the above, e.g.,MgO combined with MgTiO₃, MgO combined with MgSrZrTiO₆, MgO combinedwith Mg₂SiO₄, MgO combined with Mg₂SiO₄, Mg₂SiO₄ combined with CaTiO₃and the like.

[0080] Additional minor additives in amounts of from about 0.1 to about5 weight percent can be added to the composites to additionally improvethe electronic properties of the films. These minor additives includeoxides such as zirconnates, tannates, rare earths, niobates andtantalates. For example, the minor additives may include CaZrO₃, BaZrO₃,SrZrO₃, BaSnO₃, CaSnO₃, MgSnO₃, Bi₂O₃/2SnO₂, Nd₂O₃, Pr₇/O₁₁, Yb₂O₃,Ho₂O₃, La₂O₃, MgNb₂O₆, SrNb₂O₆, BaNb₂O₆, MgTa₂O₆, BaTa₂O₆ and Ta₂O₃.

[0081] Thick films of tunable dielectric composites can compriseBa_(1-x),Sr_(x),TiO₃, where x is from 0.3 to 0.7 in combination with atleast one non-tunable dielectric phase selected from MgO, MgTiO₃,MgZrO₃, MgSrZrTiO₆, Mg₂SiO₄, CaSiO₃, MgAl₂O₄, CaTiO₃, Al₂O₃, SiO₂,BaSiO₃ and SrSiO₃. These compositions can be BSTO and one of thesecomponents or two or more of these components in quantities from 0.25weight percent to 80 weight percent with BSTO weight ratios of 99.75weight percent to 20 weight percent.

[0082] The electronically tunable materials can also include at leastone metal silicate phase. The metal silicates may include metals fromGroup 2A of the Periodic Table, i.e., Be, Mg, Ca, Sr, Ba and Ra,preferably Mg, Ca, Sr and Ba. Preferred metal silicates include Mg₂SiO₄,CaSiO₃, BaSiO₃ and SrSiO₃. In addition to Group 2A metals, the presentmetal silicates may include metals from Group 1A, i.e., Li, Na, K, Rb,Cs and Fr, preferably Li, Na and K. For example, such metal silicatesmay include sodium silicates such as Na₂SiO₃ and NaSiO₃—5H₂O, andlithium-containing silicates such as LiAlSiO₄, Li₂SiO₃ and Li₄SiO₄.Metals from Groups 3A, 4A and some transition metals of the PeriodicTable may also be suitable constituents of the metal silicate phase.Additional metal silicates may include Al₂Si₂O₇, ZrSiO₄, KalSi₃O₈,NaAlSi₃O₈, CaAl₂Si₂O₈, CaMgSi₂O₆, BaTiSi₃O₉ and Zn₂SiO₄. Tunabledielectric materials identified as Parascan™ materials, are availablefrom Paratek Microwave, Inc. The above tunable materials can be tuned atroom temperature by controlling an electric field that is applied acrossthe materials.

[0083] In addition to the electronically tunable dielectric phase, theelectronically tunable materials can include at least two additionalmetal oxide phases. The additional metal oxides may include metals fromGroup 2A of the Periodic Table, i.e., Mg, Ca, Sr, Ba, Be and Ra,preferably Mg, Ca, Sr and Ba. The additional metal oxides may alsoinclude metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferablyLi, Na and K. Metals from other Groups of the Periodic Table may also besuitable constituents of the metal oxide phases. For example, refractorymetals such as Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta and W may be used.Furthermore, metals such as Al, Si, Sn, Pb and Bi may be used. Inaddition, the metal oxide phases may comprise rare earth metals such asSc, Y, La, Ce, Pr, Nd and the like.

[0084] The additional metal oxides may include, for example,zirconnates, silicates, titanates, aluminates, stannates, niobates,tantalates and rare earth oxides. Preferred additional metal oxidesinclude Mg₂SiO₄, MgO, CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgAl₂O₄, WO₃, SnTiO₄,ZrTiO₄, CaSiO₃, CaSnO₃, CaWO₄, CaZrO₃, MgTa₂O₆, MgZrO₃, MnO₂, PbO, Bi₂O₃and La₂O₃. Particularly preferred additional metal oxides includeMg₂SiO₄, MgO, CaTiO₃, MgZrSrTiO₆, MgTiO₃, MgAl₂O₄, MgTa₂O₆ and MgZrO₃.

[0085] The additional metal oxide phases may alternatively include atleast two Mg-containing compounds. In addition to the multipleMg-containing compounds, the material may optionally include Mg-freecompounds, for example, oxides of metals selected from Si, Ca, Zr, Ti,Al and/or rare earths. In another embodiment, the additional metal oxidephases may include a single Mg-containing compound and at least oneMg-free compound, for example, oxides of metals selected from Si, Ca,Zr, Ti, Al and/or rare earths.

[0086] This invention provides minimal loss auto-adjusting matchingcircuits for application to microwave transmission line devices thatutilize a bias voltage for tuning. Each embodiment of the auto-adjustingmatching circuit is comprised of a microwave transmission lineconfiguration, a tunable dielectric material, means for connecting to abias voltage, and a non-tunable low-loss dielectric material. Inoperation, the auto-adjusting matching circuit is placed adjacent to thetunable microwave device in order to reduce the reflections fromimpedance mismatch.

[0087] The invention contemplates various dielectric materials, tunabledielectric materials, tunable liquid crystals, bias line geometries,matching stages, impedances of microstrip lines, and operatingfrequencies of the auto-adjusting matching circuit. It should beunderstood that the foregoing disclosure relates to only typicalembodiments of the invention and that numerous modifications oralternatives may be made therein by those skilled in the art withoutdeparting from the scope of the invention as set forth in the appendedclaims.

What is claimed is:
 1. An impedance matching circuit comprising: aconductor line having an input port and an output port; a groundconductor; a tunable dielectric material positioned between a firstsection of said conductor line and said ground conductor; a non-tunabledielectric material positioned between a second section of saidconductor line and said ground conductor; and an adjustable DC voltagesource for applying a DC voltage between said conductor line and saidground conductor.
 2. The impedance matching circuit of claim 1, wherein:the conductor line is a multi-step microstrip line; and the groundconductor comprises a ground plane.
 3. The impedance matching circuit ofclaim 2, wherein: the first section of the multi-step microstrip line isdeposited on said tunable dielectric material; the second section of themulti-step microstrip line is deposited on said non-tunable dielectricmaterial; and the first and second sections of the multi-step microstripline are connected in series to form a tunable microstrip impedancetransformer.
 4. The impedance matching circuit of claim 3, furthercomprising: multiple pairs of microstrip sections functionallyinterposed between said first section and said second section of saidmulti-step microstrip line; each pair of microstrip sections includes amicrostrip section on a tunable dielectric material which is connectedin series with a microstrip section on a non-tunable dielectricmaterial; and the pairs of microstrip sections together with said firstand said second sections of the multi-step microstrip line are connectedin series to form a cascaded network.
 5. The impedance matching circuitof claim 1, wherein: the conductor line is a multi-step stripline; andthe ground conductor is a first ground plane and a second ground plane.6. The impedance matching circuit of claim 5, wherein: the first sectionof the multi-step stripline is deposited within said tunable dielectricmaterial located between said first ground plane and said second groundplane; the second section of the multi-step stripline is depositedwithin said non-tunable dielectric material located between said firstground plane and said second ground plane; and the first and secondsections of the multi-step stripline are connected in series to form atunable stripline impedance transformer.
 7. The impedance matchingcircuit of claim 6, further comprising: multiple pairs of striplinesections functionally interposed between said first section and saidsecond section of said multi-step stripline; each pair of striplinesections includes a microstrip section deposited within a tunabledielectric material which is connected in series with a microstripsection deposited within a non-tunable dielectric material; and thepairs of stripline sections together with the said first and said secondsections of the multi-step stripline are connected in series to form acascaded network.
 8. The impedance matching circuit of claim, wherein:the conductor line is a center conductor; the ground conductor is acylindrical outer ground conductor; and the center conductor iscoaxially aligned with said cylindrical outer ground conductor.
 9. Theimpedance matching circuit of claim 8, wherein: the first section of thecenter conductor is imbedded in the tunable dielectric material; thesecond section of the center conductor is imbedded in the non-tunabledielectric material; the first and second sections of the centerconductor are connected in series to form a tunable co-axialtransmission line impedance transformer.
 10. The impedance matchingcircuit of claim 9, further comprising: multiple pairs of centerconductor sections functionally interposed between said first sectionand said second section of said center conductor; each pair of centerconductor sections includes a conductor section in a tunable dielectricmaterial which is connected in series with a conductor section in anon-tunable dielectric material; the pairs of center conductor sectionstogether with the said first and said second sections of the centerconductor are connected in series to form a cascaded network.
 11. Theimpedance matching circuit of claim 1, wherein: the tunable dielectricmaterial is a barium strontium titanate composite.
 12. The impedancematching circuit of claim 1, wherein the tunable dielectric materialincludes a material selected from the group of: Ba_(x)Sr_(1-x)TiO₃,Ba_(x)Ca_(1-x)TiO₃, Pb_(x)Zr_(1-x)TiO₃, lead lanthanum zirconiumtitanate, PbTiO₃, BaCaZrTiO₃, NaNO₃, KNbO₃, LiNbO₃, LiTaO₃, PbNb₂O₆,PbTa₂O₆, KSr(NbO₃) and NaBa₂(NbO₃)5KH₂PO₄.
 13. The impedance matchingcircuit of claim 12, wherein the tunable dielectric material furtherincludes a material selected from the group of: MgO, MgAl₂O₄, MgTiO₃,Mg₂SiO₄, MgZrO₃, CaSiO₃, MgSrZrTiO₆, CaTiO₃, Al₂O₃, SiO₂, BaSiO₃ andSrSiO₃, and combinations thereof.
 14. The impedance matching circuit ofclaim 12, wherein the tunable dielectric material further includes amaterial selected from the group of: zirconnates, tannates, rare earths,niobates, tantalates, CaZrO₃, BaZrO₃, SrZrO₃, BaSnO₃, CaSnO₃, MgSnO₃,Bi₂O₃/2SnO₂, Nd₂O₃, Pr₇O₁₁, Yb₂O₃, Ho₂O₃, La₂O₃, MgNb₂O₆, SrNb₂O₆,BaNb₂O₆, MgTa₂O₆, BaTa₂O₆ and Ta₂O₃.
 15. The impedance matching circuitof claim 1, wherein said impedance matching circuit can maximize thepower transfer from a microwave source to a tunable microwave device.16. The impedance matching circuit of claim 15, wherein said tunablemicrowave device includes a tunable phase shifter, a tunable delay lineor a tunable filter.
 17. The impedance matching circuit of claim 15,wherein said tunable microwave device operates in a range from 500 MHzto 40 GHz.
 18. The impedance matching circuit of claim 1, wherein saidimpedance matching circuit can maximize the power transfer to amicrowave load from a tunable microwave device.
 19. The impedancematching circuit of claim 18, wherein said tunable microwave deviceincludes a tunable phase shifter, a tunable delay line or a tunablefilter.
 20. The impedance matching circuit of claim 18, wherein saidtunable microwave device operates in a range from 500 MHz to 40 GHz.